CH. Vl] CONICAL FORM 65 



tapering from base to apex is more pronounced and 

 gradual, approaching the form of a narrow elongated 

 cone (Fig. 1). Close examination of the cases cited shows, 

 however, that the general form is arrived at very differ- 

 ently. In the Lombardy Poplar and tall Cypress, the 

 main stem gives off branches, and these twigs, which 

 stand almost erect and approximate one against the 

 other more or less like a huge bundle of branches tied up 

 with a string; in the Cypress all arising from a common 

 stem which can be traced through to the top, but in the 

 Poplar often from main branches into which the trunk 

 breaks up, as it were, losing its individuality in pro- 

 portion as these limbs assert theirs. In the Pines and 

 Firs an important difference is expressed in the fact that 

 from a main straight stem running through to the apex 

 of the tree, the branches come off at nearly right angles 

 (Fig. 1) and in radiating groups of about five or six at 

 definite levels, that is to say, in whorls : here, then, the 

 columnar or long-conical shape of the crown is due to the 

 lower branches being somewhat longer than those of 

 the next whorl above, these slightly longer than those 

 next further up and so on to the top, a totally different 

 arrangement from that of the Lombardy Poplar. 



A pointed crown depends on the persistent up-growth 

 of the leader, or apex of the stem, projecting somewhat 

 beyond the branches. 



But in most cases there soon comes a period when the 

 on-growth of the leader is discontinued, either from in- 

 ternal causes or from accident, and the branches below 

 tend more and more upwards and outwards, and so round 

 off the apex, and it is the rule in Pines and Firs that 

 after a certain height has been attained the lateral 

 branches do this, and often in such a way that the 

 gradually shorter and shorter branches up the tree attain 

 w. V. 5 



